The present invention relates to elevator systems and, more particularly, to a platform stabilization coupler to transmit accelerations generated from an elevator system to an elevator platform.
To enhance passenger comfort, elevator systems require acceleration control systems to suppress accelerations, e.g., vibrations, transmitted from various components of the elevator system to the elevator car. The elevator car includes an elevator cab mounted on an elevator platform upon which passengers stand. The elevator car also includes an elevator car frame upon which the platform is disposed. Elastomeric isolation pads separate the platform from the frame for sound isolation purposes.
One factor that greatly affects elevator car ride quality is lateral vibration of the elevator car and its associated elevator car platform with respect to the hoistway or elevator guide rails. Lateral vibrations can be caused by aerodynamic forces acting directly on the elevator car during movement. Lateral vibrations may also be attributable to suspension forces resulting from imperfections in the manufacture and installation of the hoistway guide rails, or due to misalignment of the rails caused by the building settlement.
Active-guidance control systems have been employed to reduce or eliminate such lateral vibrations associated with elevator car movement. By way of example, the Active Roller Guide (ARG) control system was designed by Otis Elevator Company as a modernization product that could be deployed across a wide variety of gearless elevator platforms and car frames. The objective of the ARG is to reduce rail and windage induced vibrations to a maximum level of 10 mg at the center of the platform by means of a closed loop, acceleration feedback control. The closed loop design typically includes an acceleration sensor mounted either on the elevator car frame or to the platform, which generates acceleration signals indicative of accelerations at the car frame along a lateral axis. A controller, responding to the acceleration signals, then generates an opposing acceleration force from the rail toward the car frame along the same axis, with an objective of causing a net car frame acceleration of zero.
Referring to FIG. 1, a prior art elevator car two mass block diagram having a typical active guidance system with isolation pads in its feedback path is shown. It can be seen that forces F0 generated from the rail, e.g., from rail misalignment or generated as feedback from a controller, are coupled to the cab/platform mass M1 by two spring/damper pairs: C1, K1 and C2, K2. C2 and K2 are due to the roller guides as the force F0 is transmitted from the guide rails, through the roller guides and to the mass M2 of the elevator car frame. By nature of their design, the damping coefficient C2 and spring constant K2 of the roller guides is substantially constant and known. On the other hand, C1 and K1 are due to the isolation pads between the car frame and the platform, and are not constant or known.
The isolation pads, therefore, are a critical element in the feedback path of the ARG since they provide coupling, i.e., a vibration transmission path, between the car frame and platform. Their primary function is to provide sound isolation from the car frame. Their secondary function is to serve as vertical compression springs in a discrete step load sensor for dispatching and overload sensing purposes. However, the isolation pads where not designed to act as vibration couplers for an acceleration control system. This is because the spring rate K1 and damping coefficient C1 of the isolation pads are inherently variable from elevator system to elevator system due to variations in the manufacturing process. Additionally, the spring rate K1 and damping coefficient C1 do not remain constant over time in that they vary with temperature and aging effects. These variations make the adjustment of the closed loop control difficult to achieve without extensive testing at installation.
The combination of the elevator cab effective mass M1 and the spring rate K1 and damping coefficient C1 of the isolation pads determine a critical resonant mode of the platform termed the plateau resonance. This resonance is in a wide band from approximately 10 to 15 Hz. Because of this resonance condition, large phase and gain displacements are produced, e.g., 50 degrees and 10 dB, which are difficult to suppress by a constant compensation approach. Since the plateau resonance is different between elevator systems, extensive and time consuming in field survey testing is required to properly adjust the control loop gain and phase characteristics for each system.
There is a need therefore, for an improved vibration coupling system between the elevator car frame and the elevator platform.
This invention offers advantages and alternatives over the prior art by providing a platform stabilization coupler for transmitting accelerations, e.g., vibrations to an elevator platform on an elevator car frame. Advantageously, the coupler bypasses the sound isolation pads in the vibration feedback path of an acceleration control system. The coupler provides predetermined and substantially constant damping coefficients and spring constants between the platform and elevator car frame in lieu of the inherently variable damping coefficient and spring constants of the isolation pads. The coupler also allows the freedom of vertical movement required of the platform relative to the car frame to enable the isolation pads to perform their primary functions of sound isolation and load sensing.
These and other advantages are accomplished in an exemplary embodiment of the invention by providing a platform stabilization coupler for transmitting acceleration forces to an elevator platform disposed on an elevator car frame. The coupler includes a vibration member having a first surface disposed in fixed relation to either one of the elevator car frame and the platform. The coupler additionally includes a linear bearing disposed in fixed relation to a second surface of the vibration member. The bearing is disposed in moveable relation with the other of the elevator car frame and the platform to allow substantially vertical movement of the platform relative to the elevator car frame. The vibration member and linear bearing provide a transmission path for the acceleration forces from the elevator car frame to the platform. The coupler comprises a predetermined and constant spring constant and damping coefficient.
In an alternative exemplary embodiment a plurality of platform stabilization couplers disposed between the platform and the elevator car frame substantially hold the lateral movement of the platform relative to the elevator car frame within predetermined limits. The limits may be adjusted to be very small, i.e., zero lash, so that the platform and car frame move as one mass.